Hysteresis Motors Stator Rotor same as for induction motor Smooth cylinder

Principle of Operation Stator Flux establishes these magnetic poles Rotor poles “induced” by Stator Flux

Spin the stator poles with the rotor blocked Rotor poles follow the rotating flux, but lag behind by angle δh Stator poles moving CCW

Spin the stator poles with the rotor blocked If the rotor is released, it will accelerate to synchronous speed

Hysteresis Power Loss, Ph where fr = frequency of flux reversal in the rotor (Hz) Bmax = maximum value of flux density in the air gap (T) Ph = heat-power loss due to hysteresis (W) kh = constant

Mechanical Power developed

Mechanical Power Developed (cont) Independent of frequency and speed!

Hysteresis Motor at Synchronous Speed No load and negligible rotational losses Induced rotor magnets remain locked with the rotating poles produced by the stator

Hysteresis Motor at Synchronous Speed The rotor slows down and the induced rotor magnets lag the rotating poles of the stator by an angle δmag . The rotor returns to synchronous speed at the new torque angle. Apply a step increase in shaft load.

Hysteresis Motor at Synchronous Speed If shaft load causes δmag>90°, the rotor pulls out if synchronism, the magnet torque drops to zero, and the machine develops hysteresis torque. This torque is not sufficient to carry the load.

Torque-Speed Characteristic Constant Hysteresis Torque allows the motor to synchronize any load it can accelerate “Normal” Operating Range